Cell Structure and Cell Organelles

The Endoplasmic Reticulum

The endoplasmic reticulum (ER) is a network of membrane-bound tubes and cisternae
connected to the cell nucleus through the nuclear pores. It
pervades the entire cell. The rough ER is covered by ribosomes (RER); the smooth ER is not.
The ER modifies proteins and transfers substances to the Golgi apparatus.

Fig.1

Endoplasmic reticulum

Abbreviated ER.

Heavily branched network of tubes and cisternae surrounded by the ER
membrane, which is an extension of the nuclear membrane.

Most of its surface is occupied by ribosomes (rough ER). This area is
involved in translation, folding, modification, and transport of proteins. The part
of the ER with no ribosomes is the smooth ER; it is involved in large molecule
transport, in conjunction with the Golgi apparatus (dicytosome). Also fatty acid and
lipid synthesis.